Monobasically sulfated vinyl copolymers as silver halide stabilizers



United. States Patent O No Drawing. Filed Apr. 4, 1966, Ser. No. 539,735 Int. Cl. G03c N34 US. Cl. 96-109 7 Claims This invention relates to silver halide emulsions and more particularly to functional addenda for silver halide emulsions and to photographic silver halide emulsions containing such addenda.

It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called fog, and sometimes called chemical fog when it is necessary to distinguish between it and the eifects of accidental exposure to radiation; in this invention, we are not concerned with the latter.

Fog depends both on the emulsion and the conditions of development; for a given emulsion it increases with the degree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperatures or humidity or both. It is, of course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it

is frequently non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While antifoggants and stabilizers may protect, to some extent, against such effects, it is normally understood that an anti-foggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both.

Previously various non-polymeric stabilizers have been incorporated in silver halide emulsions to reduce fog. While these non-polymeric fog stabilizers have in many instances produced satisfactory results, they suffer from the disadvantage that, being non-polymeric they may migrate to another layer during coating or storage or be leached from the particular layer in which they are incorporated during processing of the coated emulsion layer.

One object of our invention is to provide fog inhibiting agents for silver halide emulsions. Another object of our invention is to provide silver halide emulsions containing novel functional addenda. A further object of our invention is to provide silver halide emulsions containing such addenda which will not migrate from the layer in which they are incorporated during coating or storage, and are not leached from that layer during processing of the coated emulsion layer. Still another object of our invention is to provide silver halide emulsions containing polymeric addenda, which in some emulsions produce sig- 'ice nificant speed increases. Other objects of our invention will appear herein.

These and other objects of our invention are accomplished by incorporating in the silver halide emulsion a small amount, relative to the entire emulsion composition, of a salt of a monobasically sulfated synthetic vinyl polymer.

One class of antifogging agents useful in the present invention consists of salts of synthetic polyvinyl resins that comprise a monobasically sulfated bound monomeric unit recurring in the vinyl polymer chain. The monobasically sulfated bound vinyl monomeric unit may constitute from about 5 to mol percent of the total monomer units in the polymer. An especially preferred antifogging agent of this class is the ammonium salt of monobasically sulfated polyvinyl alcohol which may also be called copoly(vinyl alcohol, vinyl hydrogen sulfate) ammonium salt.

EXAMPLE I Poly(vinyl alcohol, vinyl hydrogen sulfate) ammonium salt Into a 500 ml. three-neck flask, fitted with a mechanical stirring device, heating mantle, condenser and thermometer, was placed 22 g. (0.5 mole) of poly(vinyl alcohol), 36.4 g. (0.375 mole) of sulfamic acid and 250 ml. of N,N-dimethylformamide. This mixture was stirred and slowly heated to C. at which time solution occurred and then from the dark amber solution there separated a polymer mass. After precipitation had occurred the temperature of the reaction mixture was slowly raised to 110 C. and then cooled to 90 C. The N,N-dimethylformamide was decanted off and the soft cake was dissolved in ml. of distilled water (pH 2.2).

The aqueous polymer solution was adjusted to pH 7.0 with five percent sodium hydroxide. The polymer solution was filtered by suction through filter paper covered by a layer of filteraid. The dope was poured into acetone to precipitate the polymer. The light tan precipitate was washed with acetone and was then dried over night under reduced pressure over P 0 to give 57.4 g. of product.

Calculated for S, 22.7%. Found: 14.0% indicating approximately 61.7 weight percent reaction.

Several co-poly(vinyl-OH) (vinyl OSO ammonium salts were prepared in a similar manner, and analyzed with the results shown in Table 1.

TABLE 1 Polymer Percent S Wt. percent conversion 1 1 Calculated as ammonium salt.

Samples of the polymer salts were added to separate portions of a high speed silver bromoiodide emulsion which had been panchromatically sensitized with cyanine dye. Control emulsions containing no polymer salts were prepared. Each emulsion sample was coated on cellulose acetate film support at a silver coverage of 460 mg. per square foot and a gelatin coverage of 1040 mg. per square foot. Samples of each coating were tested while the emulsions were fresh, and other samples of the same emulsions were incubated for two weeks at 120 F. and then tested. In the test, the samples were exposed on an Eastman lB sensitometer, developed, fixed, washed, and dried by conventional procedure. Photographic properties of the developed samples were analyzed. Results are shown lose acetate film support at coverage of 460 mg. silver per square foot, 1040 mg. gelatin per square foot. Sam ples of each coating were exposed on an Eastman 1B sensitometer, developed, fixed, washed, and dried by a standard procedure. Photographic properties of the finished samples were analyzed. Other samples of the same emulsions were incubated for two Weeks at 120 F. and then developed and analyzed as before. Results of the test are shown in Table 3.

TABLE 3 in Table 2.

Cone, Fresh tests Z-week me. at 120 F. TABLE 2 Polymer g./mole ag. Rel. 'y Fog Rel. 'y Fog Cone, Fresh tests 2-week me. at 120 F. speed speed Polymer gJmole ag. Rel. 'y Fog Rel. Fog Control speed sample 100 1.05 0.10 40 0.62 0.61

Sample con 1. 05 10 11.2 69 97 taining 1.15 .09 74.0 1.30 .09 polymer 45.0 107 1.17 0.13 68 0.97 0.15 1.117 .09 1.252 1. 5 .10 .6 1.35 .10 76.0 1.25 .08 The results demonstrate the fog stab1l1ty achieved with 32-8 5; 9g silver halide emulsions contalmng these polymers. More- The results given in Table 2 demonstrate that copoly- (vinyl alcohol, vinyl hydrogen sulfate) salts were effective as fog stabilizers and did not adversely affect speed or gamma.

In another example to illustrate the invention, we use a vinyl copolymer which contains the vinyl hydrogen sulfate and vinyl alcohol monomer with other monomers.

EXAMPLE II Copoly(vinyl alcohol, vinyl hydrogen sulfate, vinyl 2- hydroxy-S-sulfophenyl carbonate) sodium salt Into a 500 ml., 3-neck flask fitted with a mechanical stirrer, thermometer and a heating mantle were placed 10 g. of copoly(vinyl alcohol, vinyl catechol carbonate) (0.107 mole), 9.0 g. sulfamic acid (0.097 mole) and 150 ml. of N,N-dimethylacetamide. The flask contents were stirred vigorously while heating to 60-70 C. and a viscous yellow solution formed. The reaction solution became hazy as the temperature rose past 70 C. Heating was continued to 90 C. at which time the flask contents were rapidly cooled to room temperature in a crushed ice-Water bath. The total heating time was ten minutes.

The viscous dope was poured into 3.3 liters of vigorously stirred acetone. The fibrous precipitate which was obtained was allowed to settle. The polymer was collected on a Buchner funnel, washed with acetone, and dried at C. over CaCl in a constantly applied water pump vacuum for three days.

A yield of 15.3 g. of product was obtained; 14.0 g. of the above polymer was dissolved in 100 ml. of distilled water. The aqueous dope, now at pH 1.85, was cooled to 10 C. and the pH was adjusted to 5.7 with 12 percent sodium hydroxide. The final solids content was 12.49 percent.

Calculated for SO Na CnHzzNazOnSz:

S, 13.9. Found: S, 12.4.

The polymer was added to a higlvspeed silver bromoiodide emulsion which had been panchromatically sensitized with a cyanine dye. A control emulsion was also prepared. Each emulsion sample was coated on a celluover, the results shown that the speed and gamma of the silver halide emulsions stabilized with the polymers of the invention was not adversely affected. In addition, tests of sample layers containing these polymers demonstrated that the polymers would not migrate to an adjacent layer within the photographic element, and were not leached from the layer during processing of the emulsion.

EXAMPLE III Preparation of the NH Na salt of monobasically sulfated poly(N-p-hydroxyethylacrylamide) lllHCHzCHzOSOgNH4-NB NHCHzCHzOH Into a 500 ml., 3-neck flask, fitted with mechanical stirrer, thermometer, condenser and heating mantle was placed 11.5 g. (0.10 mole) of N-fi-hydroxyethylacrylamide, 13.8 g. (0.15 mole) of sulfamic acid and 250 ml. of N,N-dimethylformamide. The reaction mixture was heated with stirring to a homogeneous solution at 36 C. Heating was continued as the reaction solution became hazy at 108 C. The heat was removed as the temperature reached 120 C. and the flask contents were cooled to 40 C.

To the reaction mixture was added 0.05 g. of azobis (isobutyronitrile) and heating was resumed with good stirring. The reactants were heated to 120 C. over an 18- minute period with a small amount of polymer starting to separate out at C. The mixture was cooled to room temperature and the separated polymer was removed by filtration. The dope was poured into 3 liters of acetone to precipitate the product. The product was filtered onto a Buchner, washed with acetone, and dried in a 40 C. oven at reduced pressure. Yield, 18.1 g. The sulfur content of the polymer was 12.7 percent indicating that 84 percent of the product as the ammonium salt was combined in the polymer. Inherent viscosity in water was 0.21. Seventeen and one-tenth grams of the dried polymer was dissolved in 45 g. of distilled water and adjusted to pH 6.0 with 5 percent aqueous NaOH. The solids content was 23.2 percent.

Also prepared was the mixed ammonium-sodium salt of monobasically sulfated poly[a-(hydroxymethyl)ethyl acrylate].

(CHgC H-) (-0H,o H)

0 H2 0 H 0 H2O SOzgNHu-NB Into a 1-liter, l-neck flask was placed 500 ml. of dried benzene, 39.3 g. of distilled [a-(hydroxymethyD-ethyl acrylate] (0.3 mole) and 0.05 g. of azobis(isobutyronitrile). The flask was fitted with a condenser and immersed into a 90 C. constant temperature bath to reflux for 22 hours. The benzene was decanted from the precipitated polymer and the residual benzene was evaporated under reduced pressure at 60 C. A sample of the polymer was removed and dried under vacuum at 45 C. The inherent viscosity in acetone at a concentration of 0.25 g. per 100 ml. of solution was 0.11.

The residue in the flask was dissolved in 150 ml. of N,N dimethylformamide and heated in a flask, equipped with a stirrer, thermometer and heating mantle, after the addition of 29.8 g. (0.31 mole) of sulfamic acid. At 42 C. a homogeneous solution was obtained and at 88 C. the reaction solution became very hazy and there was a rapid temperature rise to 117 C. The hazy reaction solution was cooled to 25 C. and isolated by pouring it into 4 liters of stirred acetone. The precipitate was filtered onto a Buchner funnel, washed with acetone and dried at reduced pressure at 40 C. over CaCl Yield, 56.2 g. The sulfur content of the polymer was 10.8 percent indicating that 76.5 percent of the product as the ammonium salt was combined in the polymer. Inherent viscosity in water was 0.36.

Twenty-five grams of the dried polymer were dissolved in 75 ml. of distilled water and adjusted to pH 6.6 with 5 percent aqueous NaOH. The solids content as determined by drying a sample at 110 C. was 19.3 percent.

Samples of the two copolymers whose preparations are described above were added to separate portions of a high-speed silver bromoiodide emulsion which had been panchromatically sensitized with a cyanine dye. Control emulsions were also prepared. Each emulsion sample was coated on cellulose acetate film support with silver coverage of 460 grams silver per square foot and gelatin coverage of 1040 milligrams per square foot. Samples of each coating were exposed on an Eastman 1B sensitometer and then developed, fixed, washed, and dried by conventional testing procedures. Photographic properties of the finished samples were analyzed. Results are tabulated in Table 4. Samples of each emulsion coating were incubated for two weeks, at 120 F. and then exposed, developed, fixed, washed, and dried as before. Results of the analysis of these samples are also tabulated in Table 4.

The test results, particularly for the incubated samples, show the monobasically sulfated vinyl polymers effected substantial reduction in fog density without adversely affecting speed or gamma. The incubated samples containing the antifogging agent also exhibited some improvement in speed retention.

Although the molecular weight of the polymers employed in our invention may be varied over a considerable range, we have found polymers prepared from commercial low molecular weight poly(vinyl alcohol) highly advantageous. Similarly, the concentration of the polymer in silver halide emulsions may be varied over a considerable range to provide fog stability. Concentrations in the range from 1 to 75 grams of polymer per mole of Ag may produce antifogging effect.

The preferred polymers of our invention are copoly- (vinyl alcohol, vinyl hydrogen sulfate) salts, which may also be referred to as partially monobasically sulfated polyvinyl alcohol salts but we have shown that other monobasically sulfated vinyl copolymers are also useful. The most useful monobasically sulfated vinyl polymers are those which contain about 5-75 mole percent of the monobasically sulfated monomer; particularly good results are achieved with polymers having 10-50 mole percent monobasically sulfated monomer. The salt forming substituent advantageously is ammonium or alkali metal, although any salt forming group may be used which does not interfere with the photographic emulsion in which the polymer is incorporated.

The photographic emulsions obtained in accordance with our invention may be sensitized using any of the well-known techniques in emulsion making, for example, by digesting with naturally active gelatin or various sulfur compounds. The emulsions may be sensitized with salts of noble metals of Group VIII of the periodic table which have an atomic weight greater than 100.

The emulsions of the invention may also contain gelatin plasticizers, hardeners and coating aids which have been described in the prior art.

The emulsions obtained in accordance with the invention may have incorporated therein addenda which make them particularly useful in various types of photographic emulsions. These emulsions may be useful in X-ray and other non-optically sensitized emulsions, and may also be used in orthochomatic, panchromatic and infrared sensitive emulsions. The addenda may be added to the emulsion before or after sensitizing dyes, if any are used. Various silver salts may be used as a sensitive salt, such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobromide or silver bromoiodide. The emulsions may be used in photographic elements intended for color photography, and thus may contain color forming couplers, or used as emulsions to be developed by solutions containing couplers or other color generating materials, or emulsions of the mixedpacket type, as described in US. Patent 2,698,794, or emulsions of the mixed grain type as described in US. Patent 2,592,243.

The emulsions obtained in accordance with our invention may be used in diffusion transfer processes which utilize the undeveloped silver halide in non-image areas of the negative to form a positive by dissolving the undeveloped silver halide and precipitating it on a silver layer in close proximity to the original silver halide emulsion layer. The emulsions may also be used in color transfer processes which utilize a diffusion transfer of an imagewise distribution of developer, coupler or dye, from a light-sensitive layer to a second layer, while the two layers are in close proximity to one another.

A wide variety of dispersing agents for silver halide grains may be employed including gelatin, other colloidal materials such as colloidal albumen, cellulose derivatives, synthetic resins, for instance polyvinyl com pounds. Some typical colloids which may be used are, for example, poly(vinyl alcohol), partially hydrolyzed p0ly(vinyl acetate), far hydrolyzed cellulose ester, watersoluble ethanolarnine cellulose acetate, polyacrylamide having a combined acrylamide content of 3-60 percent, a vinyl alcohol polymer containing urethane carboxylic acid groups or containing cyano-acetyl groups, or polymeric material which results from polymerizing a protein or saturated acylated protein with a monomer having a vinyl group such as described in US. Patent 2,852,382.

In addition to their utility in photographic silver halide emulsions as fog stabilizers, the sulfated vinyl polymer addenda of the present invention are useful in some photographic emulsions for increasing photographic speed. Particularly, in relatively low-speed, fine-grain silver chlorobromide emulsions, the speed increasing function of these addenda may be more important than their antifogging function. Such use of these addenda is contemplated within the scope of the present invention.

Photographic silver halide emulsions containing the sulfated vinyl polymer addenda of the present invention can be coated on any available support material suitable for making photographic elements. Suitable support materials include paper, glass, metal, various polymeric materials such as cellulose esters, e.g., cellulose acetate, cellulose acetate butyrate, polycarbonates, polyesters, e.g., polyethylene terephthalate, polyethylene-coated supports, and the like.

This invention has been described in detail with particular reference to the preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic silver halide emulsion containing an amount effective to reduce spontaneous fog of a salt of a monobasically sulfated vinyl copolymer at least mole percent of the monomer units thereof being monomers comprising a sulfate moiety, the cations of said salt being members selected from the group consisting'of ammonium and alkali metal ions.

2. The photographic silver halide emulsion of claim 1 at least 5 mole percent of the monomer units of said copolymer consisting of vinyl hydrogen sulfate.

3. The photographic silver halide emulsion of claim 2, said monobasically sulfated vinyl copolymer consisting of copoly(vinyl alcohol, vinyl hydrogen sulfate).

4. The photographic silver halide emulsion of claim 1, the monobasically sulfated monomer units of said copolymer consisting of monobasically sulfated N-fl-hydroxyethylacrylamide.

5. The photographic silver halide emulsion of claim 1, the monobasically sulfated monomer units of said copolymer consisting of monobasically sulfated a-(hydroxymethyl)ethyl acrylate.

6. A photographic silver halide emulsion containing from 1 to grams per mol silver of a salt of a monobasically sulfated vinyl copolymer, at least 5 mole percent of the monomer units thereof comprising a sulfate moiety, the cations of said salt being members selected from the group consisting of ammonium and alkali metal.

7. The photographic silver halide emulsion of claim 2, said monobasically sulfated vinyl copolymer consisting of copoly(vinyl alcohol, vinyl hydrogen sulfate, vinyl Z-hydroxy-S-sulfophenyl carbonate).

References Cited UNITED STATES PATENTS 3,022,172 2/1962 Ohba et al. 96-114 3,168,403 2/1965 Himmelmann et al. 96-114 3,178,294 4/1965 Kinkel et al. 96-114 FOREIGN PATENTS 625,025 3/ 1963 Belgium.

NORMAN G. TORCHIN, Primary Examiner.

J. R. EVERETT, Assistant Examiner.

US. Cl. X.R 96-114 

1. A PHOTOGRAPHIC SILVER HALIDE ENULSION CONTAINING AN AMOUNT EFFECTIVE TO REDUCE SPONTANEOUS FOG OF A SALT OF A MONOBASICALLY SULFATED VINYL COPOLYLMER AT LEAST 5 MOLE PERCENT OF THE MONOMER UNITS THEREOF BEING MONOMERS COMPRISING A SULFATE MOIETY, THE CATIONS OF SAID SALT BEING MEMBERS SELECTED FROM THE GROUP CONSISTING OF AMMONIUM AND ALKALI METAL IONS. 